1. Field of the Invention
The present invention relates, generally, to torsional dampers and, more specifically, to a torsional damper having a variable bypass clutch with a centrifugal release mechanism.
2. Description of the Related Art
In automotive applications, engine torque and speed are translated between a prime mover, such as an internal combustion engine, to one or more wheels through the transmission in accordance with the tractive power demand of the vehicle. Torque converters or start-up clutches are often employed between the internal combustion engine and its associated transmission.
Torsional damping mechanisms are well known in the related art for reducing vibrations and torque pulses between the prime mover and the transmission. One torsional damping mechanism commonly known in the art includes a drive ring that forms an annular rearward facing channel and that may be mounted to a lock-up piston in the torque converter. A plurality of coiled springs are carried in the channel for the drive ring and are engaged by a driven ring mounted to the turbine shell in the torque converter. The drive ring often includes lugs that are engaged by the coiled springs. This arrangement acts to dampen torsional vibrations due to impact loads and pulsations generated between the prime mover and the transmission. Torsional dampers of this type may also be employed between the prime mover and a start-up clutch or a pair of flywheels associated with the prime mover and the transmission, respectively.
While conventional torsional dampers employed in the related art have generally worked for their intended purposes, they are known to suffer from certain disadvantages. For example, it is not uncommon that, during vehicle launch, the torsional damper is subjected to relatively high torque peaks. When this occurs, it is possible for the coiled springs to be over-compressed to the point that they “bottom out.” When this occurs, the relative rotation between the drive and driven members is described as “over-travel” and results in the generation of noise and vibration through the vehicle driveline. Over-travel is a condition of “high hysteresis” between the drive and driven members. Over-travel may be combated by employing stiffer coiled springs. However, with the increase in the stiffness of the coiled spring, there is an associated decrease in damping through the torsional damper. On the other hand, following vehicle launch and at high rotational speeds, the input and output members of the torsional damper rotate, for the most part, substantially together so that there is little or no relative rotation therebetween. Thus, the torsional damper operates in a condition of “low hysteresis.” In this operative mode, the coiled springs adequately function to absorb the minimal torque pulses and vibrations that may be generated between the prime mover and the transmission.
While there have been a number of solutions that have been proposed in the related art to address the problems associated with high hysteresis during launch and a low hysteresis during higher rotational speeds after launch, the conventionally known torsional dampers that embody these solutions typically employ a relatively high number of components and an associated increase in cost to address the operational challenges that are placed on the torsional dampers. Notwithstanding the problem of effectively damping impact loads, pulsations, torque peaks, and vibrations between the prime mover and the transmission, there is a continuous demand for weight reduction and efficiency improvements in the art of torsional damping mechanisms.
Thus, there remains a need in the art for a torsional damper that may, efficiently, and cost effectively address operational environments that generate high hysteresis at low rotational speeds and low hysteresis at high rotational speeds. In addition, there remains a need in the art for such a torsional damper that is relatively mechanically simple and that does not add prohibitive weight or cost to the torsional damper.